Graphene is a two-dimensional crystal composed of carbon atoms, and is a material that has been greatly attracting attention since being discovered in 2004. Graphene has excellent electrical, thermal, optical, and mechanical properties, and is expected to be applied in a wide range of battery materials, energy storage materials, electronic devices, composite materials, and the like.
In order to realize such an application of graphene, the efficiency in a preparation method for cost reduction, and the improvement of the dispersibility are essential issues.
As the production method of graphene, a mechanical exfoliation method, a chemical vapor deposition (CVD) method, a crystal epitaxial growth (CEG) method, and the like can be mentioned, but these methods have low productivity and are not suitable for mass production. On the other hand, an oxidation-reduction method (in which graphite oxide or graphene oxide is obtained by an oxidation treatment of natural graphite, and then graphene is prepared by a reduction reaction) can synthesize the graphene in a large amount, and is an extremely important technique for putting the graphene into practical use.
The graphene obtained as described above has high conductive performance and further has a thin flaky structure, and therefore, can increase the conductive path, and has high potential in particular as a conductive material for a battery. However, graphene is nanocarbon, and is easily aggregated. Even when prepared simply by an oxidation-reduction method, the graphene cannot be adequately dispersed and cannot exert the potential either.
Accordingly, in Patent Document 1, graphite oxide is expanded and exfoliated by heating, and flake graphite having a high specific surface area is prepared. In Patent Document 2, graphene oxide and an electrode active material for a lithium ion battery are mixed, and then the mixture is reduced by heating, and the resultant product is utilized as a conductive agent. In addition, in Patent Document 3, graphene is reduced in the presence of catechol, and highly dispersible graphene is prepared.